I have got an old Oscilloscope up and running recently and have noticed 'bursts' of signal interfering with my trace.

When observing a sine wave, the interference looks like spikes appearing anywhere across the screen, maybe two or three at a time, duration of 1 sec or so, low voltage(~mV). This interference is more obvious at low signal inputs and on a 100MHz scope. On my 40MHz el cheapo scope, the bursts of interference are visible but less so .... I am thinking that it is a power line interference.

On my Spectrum Analyser, I am also seeing an regular 'bursts' of signal .... approx 40MHz wide, centred around 20MHz, low power, 20/30dB down on -30dBM scale .... with smaller, less obvious spikes at random frequencies up to 100MHz. I cannot recall seeing this interference 6 months or so ago ... but that maybe due to not being able to use the SA properly ... not really sure about the timing.

Turned off my Powerline Adaptors(inhouse internet over power lines), NBN Modem, telephones and Fridge .... still there.

I cannot be sure if the scope and Spectrum Analyser interference is the same thing ... but my guess is that it is ..... as my new, old scope is capable of 100MHz whereas the el cheapo scope is 'stretched' beyond 15 to 20MHz despite the 40MHz label.

Location is Melbourne suburbs.

Questions .....
.... anyone else experience this???
.... any educated guesses as to the source???
.... anyone use a Powerline filter, commercial or DIY???

Thank, Ian

Yes I have seen this.

Did you switch your phone off?

Neighbour running a TV with an HDMI connection?

Most scopes spec'ed at 40MHz will still resolve 40MHz but not within calibration. Might be 20dB down!

Hi Ian,

Phones turned off??? .... do you mean Mobile or "Landline" ??? .....

"Landline" phone is now via NBN; NBN modem off, power to these phones turned off also.

Mobile phones turned off?? .... no .... still on in other room ....

.... ??????

I'd be inclined to use wide band radio receiver to see if it can be zeroed in on at a particular frequency.

If it is like the NBN box here, in order to calibrate a radio, one shuts it off. It is an admitted fact that some of the early units splattered RFI all over the place, which mine does. Naturally NBN does not want to know about it.

What you may be seeing is a computer doing a red write or a modem doing send receive, pinging the base station.

I use power line filters, but that's for RF riding on the mains. All of the computers, TV & mains test equipment is on filtered & surge protected mains.

Marc

Hi Marcc,

What power line filters do you use for filtering RF on Mains??